A wire electric-discharge machining apparatus has a machining-speed control system that increases or decreases the machining speed so that a detection value of an inter-electrode state (for example, an inter-electrode voltage and a discharge frequency) between a workpiece and a wire electrode becomes constant. Because there are many high-frequency disturbances (noise) between such electrodes, even in a case of linear machining, the detection value of the inter-electrode state may largely fluctuate.
As a measure against such fluctuation, there is a method of stabilizing the machining speed by an averaging procedure or a low-pass filtering (filtering for removing only high-frequency components) procedure. However, because the amount of machining rapidly changes in a corner machining portion, responsiveness of machining speed control cannot be ensured by the averaging procedure and the low-pass filtering procedure. Therefore, a wire electric-discharge machining apparatus described in Patent Literature 1 preliminarily predicts the change in the amount of machining to control the machining speed in the corner machining portion depending on the predicted value.